The material to be classified or to be milled consists of coarser and finer particles that are entrained in an air stream and that form the product stream introduced into a housing of an air classifier of the jet mill. The product stream is led in the radial direction into a classifier wheel of the air classifier. In the classifier wheel, the coarser particles are separated from the air stream and the air stream with the fine particles leaves the classifier wheel in the axial direction through an outflow pipe. The air stream with the fine particles to be filtered out or to be produced can then be fed to a filter in which a fluid, such as, for example, air, and fine particles are separated from each other.
From DE 198 24 062 A1, such a jet mill is known, wherein a high-energy milling jet made from superheated steam with a high flow energy is introduced into the milling chamber of the jet mill and the milling chamber has, in addition to the inlet device for the one or more milling jets, an inlet for the milling material and an outlet for the product and wherein, in the region that the milling material intersects at least one milling jet made from superheated steam, the milling jet and milling material have at least approximately the same temperature.
Furthermore, a corresponding air classifier is known, in particular, for a jet mill, e.g., from EP 0 472 930 B1. In principle, this air classifier and its operating method are extremely satisfactory.
From DE 31 40 294 C2, a method and a device are known for separating a mixture of materials into components that can be milled to different degrees. For separating a mixture of materials made from components that can be milled to different degrees into a component that is easier to mill and a component that is harder to mill, the mixture of materials is set into a fluidized state by introducing vapor or gas streams and in this way is subjected to impact crushing. The intensity of the impact crushing is set by the selection of the operating pressure, the velocity, and the direction of the jets in such a way that only the component of the mixture of materials that is easy to mill is crushed. Following the impact crushing, the mixture of materials is exposed to centrifugal force classification. By means of this classification, the component that is easy to mill is separated as fine material and the component that is difficult to mill is separated as coarse material from the non-milled mixture of materials. Here, a fluidized bed jet mill with a centrifugal force classifier above the fluidized bed is used, wherein the mill housing has an annular gap opening into a discharge chamber in the peripheral region of the centrifugal force air classifier. The annular gap is adjustable in its width by means of a concentric ring guided in the mill housing. The axes of the jet nozzles of the fluidized bed jet mill lie in one plane and intersect at one point, and the nozzle openings directed toward each other lie on a circle that is concentric to the mill housing.
DE 38 25 469 A1 discloses a method for the dispersion, crushing, or deagglomeration, and classification of solid materials with a classifying jet mill that combines a jet mill and a spiral stream classifier. The product is supplied by means of the product feeder via injector gas into a dispersing space that is defined by a cover, a milling ring, and a base plate. A milling gas that is simultaneously also a classifying gas is led into a dispersing space via a distribution space and nozzles arranged in the milling ring. This milling gas provides a targeted loading, dwell time, and cut point on the solids according to the admission pressure, amount of gas, and nozzle geometry. The dwell time and cut point can be further varied over wide limits by the feeding of secondary gas that is divided by a cone and that flows through a concentric gap. By feeding the adjustable secondary gas flow via the gap, it is possible to influence the dwell time and loading of the solids in a targeted way. The secondary stream changes the passage likelihood in a collection container and shifts the cut point within the dispersing space toward larger values. Through the concentric gap of variable width, continuous drawing of the portion that is coarse or that is difficult to disperse into the collection container is possible. By varying the milling gas pressure, the milling gas volume stream through the milling ring and various nozzle geometries, as well as the feeding of more or less secondary gas, the crushing and separation results are affected.
Furthermore, EP 1 080 786 A1 of the present inventor discloses a method for fluidized bed jet milling, a device for this method, and a system with this device. Here, for generating a centrifugal force on the fluidized bed in the region of at least one high-energy fluid stream entering into the fluidized bed, the fluidized bed is enclosed by a housing that rotates about an axis that lies at least approximately perpendicular to the one or more fluid streams that are directed essentially opposite the centrifugal force. Therefore, advantageously, the energy exchange between the solid particles that become parts of the high-energy fluid streams can begin already directly after the penetration of the high-energy streams into the fluidized bed and in general, the concentration of the solid particles within the fluid streams is improved.
The present invention has the goal of further optimizing a method for generating very fine particles by means of a jet mill.